1. Field of the Invention
The present invention relates to a process for recycling resin scrap and an apparatus therefor. In particular, it is applicable to recycling resin scrap with paint film coated, for instance, recycling vehicle bumpers.
2. Description of the Related Art
It has been required recently to recycle and re-use resin scrap. When the resin scrap comprises thermosetting resin and thermoplastic resin, for instance, when it comprises a thermoplastic resin substrate and a thermosetting resin paint film laminated on the substrate, the thermoplastic resin melts, but the thermosetting resin does not melt nor dissolve in a solvent. Accordingly, it is difficult to recycle such resin scrap. This results from the fact that thermosetting resin is cross-linked three-dimensionally therein by thermal setting.
Accordingly, there has been proposed recently a recycling process for the rein scrap which comprises a thermoplastic resin substrate and a thermosetting resin paint film laminated on the substrate. In the recycling process, the resin scrap is Finely pulverized, and the finely pulverized resin scrap is kneaded as it is with a kneader, thereby producing recycled resin composition. However, by the recycling process, the paint film cannot be fined, and cannot be melted in the kneader. As a result, the paint film comes to exist as a foreign material in the recycled resin composition. Therefore, molded products made from the recycled resin composition comes to exhibit degraded mechanical characteristics. The degraded mechanical characteristics arise sharply in impact strength. For example, when vehicle bumpers are made from the recycled resin composition, they exhibit much more deteriorated collision resistance in cold areas than those made from virgin material. Hence, there arises a problem in that the recycled resin composition can be used limitedly in minor applications only in which impact strength is not required.
Hence, the applicants of the present invention developed a new recycling process for producing recycled resin composition which is disclosed in Japanese Re-laid-open Patent Publication No. 5-801,232 based upon a PCT application. In the recycling process, resin scrap with a thermosetting resin polyurethane paint film or an amino resin paint film laminated is pulverized, and the pulverized resin scrap is hydrolyzed by heating and melting under a pressure of 35 kgf/cm.sup.2 at a temperature of up to 220.degree. C., thereby producing recycled resin composition. By the recycling process, the thermosetting resin constituting the paint film can be easily converted into low-molecular-weight compounds by the hydrolysis with the highly heated and pressurized water. After the hydrolysis, the paint film can be fined into pieces by melting and kneading the resin scrap, and the resulting fined paint film pieces can be dispersed in the recycled resin composition further uniformly. Thus, the paint film do not act as foreign material. Hence, the recycling process can advantageously give the sufficient mechanical strength to the recycled resin composition. It has been verified by infrared spectroscopy and liquid chromatography that the paint film is converted into the low-molecular-weight compounds by the hydrolysis.
In addition, as set forth in Japanese Unexamined Patent Publication (KOKAI) No. 5-200,749, another recycling process has been known. In the other recycling process, resin scrap is supplied to a kneader together with a decomposition facilitating agent, such as Lewis acid like tin chloride, alkali metal hydroxide, alkaline-earth metal hydroxide, amine and metal phosphate, it is melted and kneaded at a temperature of 200.degree. C. or more, and thermosetting resin is fined by thermal decomposition so as to disperse in recycled resin composition. According to the recycling process, the decomposition facilitating agent is added in an amount of from 0.01 to 1% by weight with respect to the resin scrap. This recycling process, however, does not utilize hydrolysis in order to recycle the resin scrap.